Macrophage iron release was greatly impaired in Fpn1^LysM/LysM mice fed an iron-deficient diet. Three-week-old Fpn1^flox/flox (3 male, 3 female) and Fpn1^LysM/LysM (3 male, 3 female) weanling mice were fed with AIN76A iron-deficient diet for 5 weeks. (A) Spleen nonheme iron concentrations, (B) total nonheme iron content in the spleen, and (C) liver nonheme iron concentrations were measured in these mice. The spleen and liver nonheme iron concentrations of 2-month-old mice (Fpn1^flox/flox, 7 male, 7 female; Fpn1^LysM/LysM, 7 male, 7 female) that were fed with normal chow diet are also presented for comparison. Data are mean ± SEM. *P < .05. †P < .001.